<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <title>Document</title>
    <style>
      .demo {
        background-color: orange;
      }
    </style>
  </head>
  <body>
    <button id="btn">点我创建一个输入框</button>

    <script type="text/javascript">
      const btn = document.getElementById("btn");
      btn.onclick = () => {
        const input = document.createElement("input");

        // 挂载元素前
        input.className = "demo";
        input.value = 99;
        input.onclick = () => {
          alert(1);
        };

        // 挂载元素
        document.body.appendChild(input);

        // 挂载元素后
        input.focus();
        input.parentElement.style.backgroundColor = "skyblue";
        console.log(input.parentElement);
      };
    </script>
  </body>
</html>
